A. A. Denisov

Plastic deformation macrolocalization during serrated creep of an aluminum-magnesium Al-6 wt % Mg alloy

The nonlinear dynamics of the space-time structure of macrolocalized deformation is studied by a set of high-speed in situ methods under the conditions of serrated creep in an aluminum-magnesium Al-6 wt % Mg alloy at room temperature. Macroscopic deformation jumps with an amplitude of several percent are detected in the creep curve of this alloy. It is found that a complex space-time structure of macrolocalized deformation bands moving in a correlated manner forms spontaneously in the material during the development of a deformation jump. The difference between the observed picture of deformation bands and the well-known Portevin-Le Chatelier classification of deformation bands is discussed.

Dynamics of deformation bands and fracture of the aluminum-magnesium alloy 5556

The dynamics of deformation bands at the prefracture stage of the aluminum-magnesium alloy 5556 has been examined using the high-speed video recording. It has been revealed that, in the artificially aged and recrystallized alloys, the correlations between the propagating deformation bands and the development of the main crack are of different character.

Serrated creep and spatio-temporal structures of macrolocalized plastic deformation

The dynamics and morphology of macrolocalized deformation bands have been investigated using a complex of high-speed in situ methods under the conditions of serrated creep of flat samples of the aluminum-magnesium alloy 5456 with different aspect ratios. It has been found that, at the front of a macroscopic plastic deformation jump, a complex structure of propagating deformation bands, which are considered as macrolocalized deformation “quanta,” is spontaneously formed in the material. It has been shown that, with an increase in the sample length, the deformation behavior of the alloy tends to the state of self-organized criticality.

Direct current induced suppression of the Portevin-Le Chatelier serrated deformation in the aluminum-magnesium alloy 5056

The effect of direct current induced suppression of the Portevin-Le Chatelier serrated deformation in the aluminum-magnesium alloy 5056 has been revealed experimentally. This effect manifests itself as an increase in the critical plastic strain, which precedes the onset of serrations in the stress-strain curve, with an increase in the current density in the range from 15 to 60 A/mm2. It has been shown that the observed effect is not related to the Joule heating of the entire specimen. Possible mechanisms of the phenomenon have been discussed.

Study of the Mechanisms of Current-Induced Suppression of Serrated Deformation

The main results of studying the influence of electric current on the Portevin‒Le Chatelier serrated deformation in some commercial aluminum alloys of the Al‒Mg, Al‒Li-Mg, Al‒Zn‒Mg‒Cu, and Al‒Cu systems are reported. It is found that the passage of a low-density (~10–60 A/mm2) dc current leads to the suppression of serrated deformation and band formation in all alloys under study, except for the Al‒Cu alloy. Possible mechanisms of this phenomenon are discussed, basically in terms of possible influence of current on the processes of precipitation and dynamic strain aging, which are used to explain the Portevin‒Le Chatelier effect.

Spectral and dynamic analysis of plastic instabilities during serrated creep of the aluminum-magnesium alloy

The force response to the development of a macroscopic plastic deformation jump under the conditions of serrated creep of the aluminummagnesium alloy 5456 has been studied using spectral and dynamic analysis methods. The flicker-noise structure of the force response indicating the self-organized criticality state has been revealed. It has been found that a short-term state of plastic instability flatter spontaneously appears during the development of the macroscopic deformation step.

Deformation chaos and self-organization at the prefracture stage of 5556 alloy

Based on the analysis of the data of high-speed video recording of the surface of the deformed aluminum-magnesium alloy 5556, it has been found that the unstable plastic deformation associated with the deformation band dynamics tends to deformation chaos with increasing deformation. It has been shown that the ductile fracture of the 5556 alloy with a recrystallized structure should be considered as a global self-organization in a nonlinear nonequilibrium system being in the state of deterministic chaos.

Investigation of the effect of electric current on serrated deformation and acoustic emission in the aluminum-magnesium alloy 5056

The effect of direct electric current on the serrated deformation of the aluminum-magnesium alloy 5056 has been studied using the acoustic emission method and high-speed video filming of propagating deformation bands. The phenomenon of the electric current-induced suppression of low-frequency acoustic emission signals has been revealed in the range of 1 Hz–2 kHz, which is connected with the development of Portevin-Le Chatelier deformation bands. The characteristic times of damping and growth of plastic instabilities and acoustic signals caused by them after current turn-on and turn-off, respectively, have been estimated.

Morphological diagram of Savart-Masson bands of macrolocalized deformation

The dynamics and morphology of Savart-Masson bands of macrolocalized deformation during a tension test of flat samples of aluminum-magnesium alloy Al-6wt.%Mg with a constant stress rate